1. Field of the Invention
This invention relates to a data storage system for reading and displaying a plurality of stored data records in a predetermined sequence and, more particularly, to a data storage system using a non-volatile memory.
2. Description of the Prior Art
RAM (random access memory) is well known in the art as a data storage for storing many data records. In the RAM, however, the power source disconnection results in loss of the stored data. In order that the stored data remain when the power supply is cut, a non-volatile memory is used.
As a non-volative memory, EEROM or the like is well known, which is capable of electrically writing and erasing data. At present, however, EEROM has a limited write repetition number. That is, when the writing is repeated for more than a predetermined number of times, no further data can be written in that area or erroneous data is written.
When it is desired to store a plurality of data records in a predetermined (e.g., alphabetical or numerical) sequence, data sorting is carried out such that those data records succeeding a new data record are moved to next storage locations while the new data record is placed at a free area thus made.
With this method, however, it is necessary to shift all data records succeeding a data record to be added. This increases a number of times of writing in the data storage areas. Therefore, the method is not suited to the EEROM or the like with a limited write repetition number.
To store ordered data records in the EEPROM, each data record is stored together with immediately preceding and succeeding, i.e., backward and forward data storage area address pointers specifying the address of next data to be read out.
With this method of data recording, it is necessary only to set the backward and forward pointers of a data record to be added and to update the forward pointer of the immediately preceding data record and the backward pointer of the immediately succeeding record. This minimizes the number of writing operations in the EEPROM.
However, in the event of the failure of such pointers, the data link disconnection occurs so that no further data records can be read out or displayed.